The victim, Solema Jubelan, 60, of the Kilusan ng Malayang Pilipino (Kampi), died while being treated in a hospital.
Jubelan was on her third and last term as provincial board member.
Inspector Benjamin Mauricio, operation and intelligence chief of the Kidapawan City police, said Jubelan’s escort, PO1 Safiro Moreno, who was seated behind her, was struggling to open the door of their Isuzu Highlander so he could alight when his gun fell from his waist and went off.
Mauricio said the bullet pierced through the front seat of the vehicle, hitting Jubelan in the lower back.
"According to attending doctors, her spinal column was hit first before the bullet penetrated her body," Mauricio said.
Mauricio said Moreno, a nephew of Jubelan, voluntarily turned himself in for investigation.
Jubelan’s relatives said they are convinced there was no "foul play" in the incident. Moreno’s mother is a sibling of Jubelan.
The elders of the Jubelan family confirmed that Jubelan’s sister, Zaida Jubelan-Rinsulat, provincial social welfare officer of North Cotabato, will replace the victim as Kampi’s congressional candidate in the second district.